The renowned Turkish novelist Aslı Erdoğan says she is facing “permanent damage” from the treatment she is receiving in prison after her arrest last week.

Erdoğan, an award-winning and celebrated Turkish novelist, was arrested in her home on the night of 16 August, according to a statement from her French publisher Actes Sud. A columnist and member of the pro-Kurdish opposition daily Özgür Gündem’s advisory board, which was shut down under the state of emergency that followed the failed coup of 15 July, her arrest came alongside that of more than 20 other journalists and employees of the paper. She was subsequently charged with “membership of a terrorist organisation” and “undermining national unity”.

Erdoğan, whom the French literary magazine Lire named as one of the 50 most promising authors of the future, told the daily Hürriyet through her lawyer, Nesrullah Oğuz, that she was being treated in prison “in a way that will leave permanent damage on my body”. She said she was sleeping in a bed that had previously been urinated in, and that she was not able to get access to her medication.

“My pancreas and digestive system don’t work properly, but my medicine has not been given to me for five days. I am diabetic and I need special nutrition. But in jail I am only able to eat yoghurt,” she said. “Also, even though I suffer from asthma and chronic obstructive pulmonary disease, I have not been allowed access to open air [since entering prison].”

Her detention has prompted a wave of calls for her release. “With the arrest of one of the nation’s most celebrated and internationally known authors, we can see that no poet, novelist, or playwright is safe in [President] Erdoğan’s Turkey,” said the novelist and translator Maureen Freely, president of English PEN, which is calling for the immediate release of those detained following the raid on Özgür Gündem “solely in connection with their work or peaceful exercise of their right to freedom of expression”.

A petition calling for Erdoğan’s release has been signed by almost 25,000 people. Describing her as “one of the world’s most notable novelists”, the petition says that “her only wish for her country is to live in a better, more democratic and civilised society”, and that she “produces work towards this wish while promoting Turkish literature globally”.

PEN International said it was “deeply concerned” for her health, describing the conditions in which she is being held as “wholly unacceptable” and calling on the Turkish authorities “to immediately provide better conditions [and] ensure immediate access to medication and to her doctors as a matter of extreme urgency”.

Sahar Halaimzai, PEN International campaigns manager, said: “The crackdown on free speech that we are witnessing in Turkey is unprecedented in the country’s modern history. The attempted coup does not justify the attack against all dissenting and critical voices. Aslı Erdoğan is one of dozens of journalists currently behind bars in Turkey, held in difficult conditions and facing an uncertain fate. We strongly urge the Turkish government to halt this assault on free speech and human rights, and comply with their obligations under international law during this period of emergency.”

Erdoğan told Hürriyet that she was aware of the solidarity being shown for her. “I’m aware that great efforts are being spent. I’m aware of the sincerity and feelings in the messages that I receive. It may sound very vain, but I thank you very much,” she said.

Her arrest follows the Turkish government’s closure of 29 publishers under the state of emergency law. The move has been condemned by publishers around the world, with the PEN International Publishers Circle saying that “while recognising the right of the Turkish authorities to investigate and prosecute those responsible for the failed coup, [we] call on the Turkish authorities not to use the state of emergency to restrict lawful freedom of expression and to ensure that writers and publishers are able to freely carry out their activities”.